I can confirm this for XP as well. I've found a number of sites that WinHTTrack
fails to mirror, with the dreaded "Open error when decompressing" error, if
WinHTTrack is being run by a non-administrative user.

That's dismaying; running WinHTTrack, or any HTTP user agent, as an
administrator is a security risk. I'd rather not depend on WinHTTrack being
completely free of exploitable vulnerabilities when I use it.

If I have time, I may pull the source and build for debug to see if I can
figure out what's going on.